UPDATE: I am finding that, as I suspected, the vast majority of the tasks that I am adding to GTM do not need a due date, as they are tasks that get done when they get done. I find that this generally works better in a Getting Things Done workflow, i.e. you can spend quite a lot of time changing the due date in tasks, which wastes time. Having the option to set a due date is great, but shouldn't be compulsory. Having the option to set High, Medium or Low Priority would be a way of organising tasks without having to enter a due date.